Conventionally, image enhancement processing for improving image quality by sharpening an image has been widely known. For example, a conventional television receiver carries out contour compensation for sharpening rising and falling of a video signal corresponding to an outline portion of an image to be displayed. The contour compensation extracts a high frequency component of an input image signal (a luminance signal), amplifies the high frequency component, and adds the amplified high frequency component to the input image signal, thereby improving visual image quality. FIG. 19 are diagrams illustrating changes in a waveform of a signal level of the image caused by the conventional image enhancement processing. FIG. 19A illustrates the waveform of the signal level in a horizontal direction of the input image signal, particularly illustrating a waveform of a portion corresponding to an edge where the signal level changes in the horizontal direction. FIG. 19B illustrates the high frequency component extracted from the input image signal. By amplifying the high frequency component and adding the amplified high frequency component to the input image signal, an output image signal with a sharp rising of the edge as illustrated in FIG. 19C may be obtained.
In recent years, also, there has been suggested a technique called super-resolution that up-converts, in particular, the input image into an output image with higher resolution and carries out the enhancement processing on the up-converted image (for example, see NPL 1 set forth below).